An Automated Assay for Carbapenemase Detection in Enterobacterales: a Real-World Performance

Background: Carbapenem-resistant Gram-negative organisms pose a significant challenge to global healthcare, making the reliable detection and classification of carbapenemases essential for informed therapy and infection control. The BD Phoenix CPO detect assay offers simultaneous carbapenemase detection and Ambler classification in routine antimicrobial susceptibility testing. Accordingly, this study analyzed real-world data on the BD Phoenix CPO test to evaluate its performance in clinical settings over a period of two years. Methods: We analyzed 298 samples using BD Phoenix CPO detect assay, Xpert Carba-R polymerase chain reaction (PCR), and conventional PCR from January 2021 through December 2022 to identify and confirm carbapenemase genes. The BD Phoenix system was used for antimicrobial susceptibility testing and carbapenemase classification. The Xpert Carba-R kit detected five key carbapenemase genes (blaKPC, blaNDM, blaVIM, blaIMP, and blaOXA-48), while conventional PCR identified these five genes and additional five carbapenemase genes (blaGES, blaSPM, blaSME, blaSIM, and blaGIM). The PCR results were compared with those from the Phoenix system. Results: Sputum was the most common specimen type, and Klebsiella pneumoniae accounted for 86.9% of the identified species. The concordance between the BD Phoenix assay and PCR for identifying carbapenemase genes showed 98.8%, 35.3%, and 71.4% agreement for Ambler class A, B, and D, respectively. The Phoenix had a false positive rate of 9.0%. Additionally, 21.2% of carbapenemase-positive cases had uncertain classifications. The concordance between Carba-R PCR and conventional PCR was 98.4%, with positive and negative agreement of 98.2% and 86.2%, respectively. Conclusions: The BD Phoenix CPO test provides a significant advantage of delivering results concurrently with antimicrobial susceptibility testing, representing a highly valuable tool for routine screening in clinical practice. Nevertheless, its high false positive rate underscores the necessity of confirmatory testing to ensure accurate carbapenemase classification.